In piggyback trains, the cross country travel is by rail and the local delivery is by truck. This effects savings of energy and of labor. However, the dead weight of the piggyback flat cars makes up a large portion of the total railway load.
It has previously been proposed to provide novel highway trailers which can be supported upon a track without the use of a piggyback flat car. One such example is shown in U.S. Pat. No. 4,202,454 issued 13 May, 1980. Another prior art design is shown in U.S. Pat. No. 2,963,986 issued 13 Dec., 1960.